The invention relates to conductive, highly abrasion-resistant coatings on mouldings, including at least one conductive layer and at least one highly abrasion-resistant layer and a process for their production and their use.
Conductive coatings based on polyethylene dioxythiophene (PEDT) already have a broad area of application, e.g, anti-static finishes for photographic films. Numerous processes have described how such conductive coatings can be produced. Basically, either the PEDT, which is mixed with a binder, is applied or a multi-layered structure is chosen which has the advantage that binder and PEDT do not have to be compatible (miscible).
Conductive and scratch-resistant multi-layered structures for coating picture tubes are described in WO 96/05606. Scratch-resistant layers, for example silicon dioxide obtained by hydrolysis and condensation of tetraethyl orthosilicate, are applied to a conductive PEDT layer, the layer thickness being limited to 50 to 250 nm. Alternatively, production of scratch-resistant layers from inorganic-organic hybrid materials is described, which layers can be applied to the conductive layer in a layer thickness of 10 xcexcm and greater. These hybrid materials are based on trialkoxysilanes of Formula Rxe2x80x2xe2x80x94Si(OR)3, wherein Rxe2x80x2 represents a polymerisable group. The multi-layered structures described in WO 96/05606 have several fundamental disadvantages however:
After applying one of the described scratch-resistant layers, a notable level of conductivity can no longer be measured on the surface of the multi-layered structure.
Although a good level of scratch resistance is found (ascertained by determining the lead pencil hardness), the abrasion resistance of the coatings is poor.
High curing temperatures, 160xc2x0 C. in the examples.
Antistatic multi-layered structures, in which the top (scratch-resistant) layer must also exhibit a certain level of conductivity, or multi-layered structures with vitreous abrasion resistance cannot therefore be produced. Furthermore, curing temperatures of 160xc2x0 C. cannot be used for coating the majority of plastics materials (softening).
Conductive coatings for transparent substrates, such as plastics materials or glass for example, must retain their optical properties undiminished under mechanical load and must therefore have high resistance to abrasion. In WO 98/25274, mixtures are described which produce conductive coatings with good adhesion and with improved scratch resistance and transmittance of visible light. These mixtures consist of a binder based on polyfunctional organosil(ox)anes and a conductive organic polymer which are known from WO 98/25274 and EP-A 0 947 520. The described binders are wherein they contain heterometals such as boron or aluminium and exhibit particularly good abrasion resistance.
In EP-A 0 947 520 it is stated that these binders react sensitively to the addition of water, so by adding PEDT for example, in the conventional form supplied (Baytron(copyright) P, approximately 1.3% dispersion of PEDT and polystyrene sulphonate in water), the processing time of these mixtures is significantly reduced. Furthermore, the addition of PEDT to the binder often leads to a loss in abrasion resistance which can clearly be seen even with highly abrasion resistant coatings.
The object of the present invention was therefore to provide conductive surfaces provided with abrasion-resistant coatings, during the production of which the above-mentioned disadvantages are avoided.
Surprisingly it has now been found that a multi-layered structure on a substrate (moulding) including at least one conductive layer and at least one highly abrasion-resistant layer still has a measurable level of electrical conductivity on the surface of a moulding even though the top, highly abrasion resistant layer is a good electrical insulator.
The invention relates to a conductive and highly abrasion-resistant coating. The coating comprises (a) a first layer comprising an electrically conductive polymer, and (b) a second layer comprising a highly abrasion-resistant layer of a polyfunctional organosil(ox)ane, wherein the coating is on a substrate of a multi-layer structure. The invention also relates to a method for making and using such a coating. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
The present invention therefore relates to conductive and highly abrasion-resistant coatings on a substrate as a result of a multi-layered structure, wherein an electrically conductive polymer is applied in a first layer and a highly abrasion-resistant layer of polyfunctional organosil(ox)anes is applied in a second layer.
The mouldings coated according to the invention have a measurable level of electrical conductivity on the surface even though the highly abrasion-resistant layer is a good insulator. The abrasion resistance of the multi-layered structure according to the invention (in the Taber abraser test) is similar to that of glass and curing can advantageously take place at temperatures lower than 160xc2x0 C.
The present invention also relates to a process for producing conductive and highly abrasion-resistant coatings, wherein a conductive layer is applied wet chemically in a first stage and a highly abrasion-resistant layer is subsequently applied in a second stage.
Highly abrasion-resistant coatings in the context of the invention are those which exhibit scattered light on the scratch mark (determined in accordance with ASTM D 1003) in the Taber abraser scratch test (determined according to ASTM D 1044, 1,000 cycles, 500 g load per wheel, CS-10-F stones) of less than 20%, preferably less than 10%, particularly preferably less than 5%. In comparison, commercially available Makrolon(copyright), for example, exhibits scattered light of more than 30% on the scratch mark even after 100 cycles in the Taber abraser test. Glass exhibits scattered light of approximately 1 to 3% after 1,000 cycles in the Taber abraser test.
Polyfunctional organosil(ox)anes in the context of the invention are linear, branched or cyclic monomeric organosil(ox)anes which have at least two silicon atoms with hydrolysable and/or condensation crosslinking groups, wherein the silicon atoms are connected to one another in each case by means of a linking constructional unit with at least one carbon atom. Examples of polyfunctional organosil(ox)anes are found inter alia in EP-A 0 947 520. Production of aluminium- and boron-containing sol-gel condensates from which coatings with particularly high abrasion resistance can be obtained is also described therein.
Sol-gel materials based on cyclic carbosiloxanes of Formula (I) 
in which
m is 3 to 6, and preferably m is 3 or 4,
o is 2 to 10, and preferably o is 2 and
a is 1 to 3,
R1 is C1-C6-alkyl, C6-C14-aryl, preferably R1 is methyl, ethyl, isopropyl and when a is 1 R1 can also represent hydrogen, furthermore when
R2 is C1-C6-alkyl, C6-C14-aryl, preferably R2 is methyl and
R3 is C1-C6-alkyl, C6-C14-aryl, preferably R3 is methyl, ethyl and particularly preferably R3 is methyl,
are used to produce highly abrasion-resistant coatings which, in addition to their high mechanical strength, also exhibit good weathering resistance.
As described in WO 98/52992 and in U.S. Pat. No. 6,005,131, the cyclic carbosiloxanes are co-condensed with tetraalkoxysilanes, organotrialkoxysilanes and/or nanoparticles, the presence of aluminium or boron alkoxides enhancing the abrasion resistance of the coatings produced from the condensates as shown in EP-A 0 947 520.
Conductive coatings in the context of the invention exhibit a surface resistance of 0.1 to 1012 xcexa9/xe2x96xa1.
Preparations of polythiophenes as they are described in DE-OS 42 11 459, EP-A 339 340 and EP-A 440 957 are preferably used as conductive layers. They contain polythiophene salts of the polythiophenem+ Anmxe2x88x92({circumflex over (=)} polyanion) type, wherein the polythiophene cation polythiophenem+ contains positively charged units of Formula (II). 
wherein
A represents a C1-C4-alkylene radical optionally substituted by C1-C20-alkyl-, xe2x80x94CH2xe2x80x94OH or C6-C14-aryl groups. The number of units in the polythiophene cation can be between 5 and 100.
Examples of polyanions which can be used according to the invention are the anions of polymeric carboxylic acids such as polyacrylic acids, polymethacrylic acids, polymaleic acids, furthermore anions of polymeric sulphonic acids such as polystyrene sulphonic acids and polyvinyl sulphonic acids. These polycarbonic acids and polysulphonic acids can also be copolymers of vinyl carboxylic acids and vinyl sulphonic acids with other polymerisable monomers such as acrylic acid esters and styrene.
The mean molecular weight Mw of the polymeric acids, from which the polyanions which can be used according to the invention are derived, is 1,000 to 2,000,000, preferably 2,000 to 500,000. The polymeric acids or their alkali metal salts are commercially available or can be produced by known processes as described, for example, in Houben-Weyl: xe2x80x9cMethoden der organischen Chemiexe2x80x9d, Volume E20, xe2x80x9cMakromolekulare Stoffexe2x80x9d, Part 2, p. 1141 et seq.
With the multi-layered structure produced according to the invention, a distinction has to be made between the conductivity of the PEDT-containing layer as such and the conductivity of the top, highly abrasion-resistant coating. As the latter is an electrical insulator, the conductivity of the entire layer structure is obviously lower than that of the PEDT layer(s) beneath it.
The simplest layer structure produced according to the invention consists of the substrate, a PEDT-containing layer and a highly abrasion-resistant top layer.
In an embodiment of the present invention, conductive and abrasion-resistant surfaces on mouldings are obtained in that a PEDT-containing layer is initially applied to the substrate and highly volatile constituents such as solvents are optionally evaporated. The highly abrasion-resistant coating is then applied with or without further curing and is finally cured by heat or irradiation.
In a further embodiment of the present invention, the surface of the substrate is treated chemically with an adhesion promoter, or physically (plasma, corona), prior to application of the conductive layer, in order to achieve improved adhesion. This is particularly important with plastics materials but may also be necessary, for example, with glass. It is, however, also possible to add the adhesion promoter to the PEDT-containing solution, whereby an additional coating stage can be avoided.
It is also possible to finally provide the multi-layered structure produced by wet chemistry according to the invention with an inorganic layer, for example, of SiO2, TiO2 or Al2O3 precipitated from the gaseous phase. As a result, the wear resistance or the anti-reflective effect can be further improved.
The conductive and highly abrasion-resistant layer can be applied by any commonly known technique, such as centrifuging, spraying, dipping, casting, knife coating or brushing.
Examples of substrates which can be provided with the multi-layered structure according to the invention include metals, ceramics, wood, glass and plastics materials such as polycarbonate.
The surfaces produced according to the invention and provided with a conductive and highly abrasion-resistant coating are used, e.g., as low radiation screens (electrical resistance of the PEDT layer less than 1,000 xcexa9/xe2x96xa1) or as antistatic and abrasion-resistant plastics materials, for example, in the form of films, extruded parts or injection mouldings. Polycarbonate, in particular, can be protected in this way from mechanical damage and electrostatic charges.
The invention is further described in the following illustrative examples in all percentages are based on weight and on the total quantity of all components used.